When a prime mover such as an internal combustion engine, turbine, or electric motor is used to power a driven device such as a generator, propeller driveshaft, compressor, or a transmission, some form of coupling is necessary to connect the rotating output of the prime mover to the rotatable input of driven device. In an ideal situation, the centerline of the rotating output of the prime mover will be coaxial to the centerline of the rotatable input of the driven device when both devices are in their normal operating condition. In most large machinery situations, it is not possible to achieve a situation close enough to the ideal to prevent machine damage without utilizing some form of flexible coupling. Even when a flexible coupling is used, it is desirable to come close to the ideal alignment to prolong the life of the coupling, prevent torsional or linear vibration problems in the machinery, and reduce the amount of energy lost as heat generated from flexing the coupling.
U.S. Pat. No. 5,684,578 to Nower et al. disclosed a laser alignment head system having two laser heads that replace the more traditional mechanical feelers. One laser head scans a first of two coupled shafts and the second laser head scans the second shaft. Data is then manipulated to determine any misalignment between the two shafts. However, this arrangement tends to be expensive and difficult to use in close coupled arrangements wherein any radial and axial clearances are usually insufficient to accommodate such cumbersome laser head system.
The traditional solution to this problem has been to align some non-rotating components on both sides of the coupling and rely on tight manufacturing tolerances in the components to ensure alignment of the rotating components. This method has two inherent problems. The first problem is that it requires the machining and assembly tolerances of up to several dozen components to be very tight so that their total tolerance stack up does not result in the rotating components being out of alignment by an unacceptable amount even when the non-rotating components are aligned. The second problem is that it does not provide positive proof of alignment. This is especially important when either of the components to be coupled are manufactured in a different location than where they are assembled. For example, if an engine manufacturer changes the allowable run out on the flywheel housing face and does not inform the generator set (“genset”) assembler, a genset made after the change may not have proper alignment of the rotating components even though the genset assembler continues to perform the alignment of the non-rotating components in the same manner which previously produced acceptable results.